This invention relates to cable spooling systems in which the cable is fed to and from the spool by a levelwind mechanism that distributes the cable along the axis of the spool. More particularly, the lateral movement of the levelwind follows the path of a pawl traveling in a groove formed as a diamond screw in the surface of a roller oriented parallel to the axis of the spool. The levelwind is connected to a load compensated hydraulic system which absorbs the transitory and constant loads on the cable thereby removing stress from the pawl.
In the general field of oceanography, there are numerous applications for towed arrays wherein a ship will pay out and retrieve cable. The applications include such diverse fields as exploration, exploitation and national defense, among others. In these fields, cables may be used to tow payloads, such as remotely operated vehicles (ROV) and SONAR arrays or the cable, itself, may serve as the operative component, such as communications, power or carrying various spaced sensors. During operations, the roll of the ship or grounding of the array may cause random surges in pressure which is transmitted by the cable to the on board equipment.
Also, the depths or distances required by these applications necessitate a handling and storage system that is compact and can manipulate heavy loads. Due to the work environment, these systems must perform repeatedly without significant maintenance.
The retrieval equipment must have a control system to compensate for the random variations of pressure required during operations and retrieval. Conventionally, the systems can be adjusted so as not to exceed the tensile strength of the cable. While this protects the cable, there also needs to be a compensation mechanism to protect the equipment.
Conventional ship board installations of cable spools require that the axis of the spool be perpendicular to the direction in which the cable is being payed out or retrieved. There is also a need for a system in which the cable spool may be placed at an angle, other than 90 degrees, to the direction of the payed out cable.
Hara et al, U.S. Pat. No. 4,143,834 discloses a wire winding device which has a levelwind operated by a feeding screw. In one embodiment, a guide roller is used with the levelwind.
Baugh et al, U.S. Pat. No. 5,950,953, discloses a cable winding apparatus having guide rollers operated by a diamond screw levelwind.
Another cable spooling system which uses a diamond screw levelwind is described in U.S. Pat. No. 4,767,073 for winding electrical cables on drilling rigs. In this system, there is a guide mechanism which has a pawl continuously traversing the diamond screw shaft to evenly distribute the cable onto the spool. The cable is payed out and retrieved through the guide in a direction perpendicular to the axis of the spool. An idler wheel, with an axle parallel to the axis of the spool, is used to reduce the cable pressure on the pawl of the diamond screw. The idler wheel is spring loaded to accept variations in the load of the paid out cable. Any sudden or prolonged increase in pulling force on the cable may overcome the resistence of the springs on the idler wheel and transmit the force to the pawl. For winding the cable on the spool, the spool is powered by a pressure-compensated hydraulic system which reacts to the pulling load on the cable to prevent damage to the cable. However, in operation, this pressure compensation is subsequent to the cable passing over the idler wheel and pawl so that the pawl will be subjected to increased loads even as the spool is stopped.
A mobile load compensated cable winding device is disclosed by Conti, U.S. Pat. No. 4,692,063, in which pressure transducers are used to control a hydraulic winding mechanism and the movement of the vehicle.
There are numerous other levelwind systems using the diamond screw guide but the conventional systems suffer from increased wear between the pawl and the diamond screw because the cable loads are transferred to the pawl.
This invention teaches an improvement to winches utilizing diamond screw levelwinds. The diamond screw levelwind, as instantly described, will allow the levelwind to operate with minimal load on the drive pawl. The diamond screw levelwind is widely utilized because of its reputation for simple and reliable mechanical operation. The problem generally encountered centers around the fact that the relatively small follower or drive pawl, which is generally formed from bronze, and which runs in the diamond groove, is limited in the load it can safely handle. If this device is utilized in high load capacity winches, very high maintenance and/or a high failure rate in the field often result. Thus in high load situations, electro-active levelwind devices are often used. A need exists for a sub-sea right angle levelwind with a fairly high line pull winch. A diamond screw type device would be an acceptable choice, but for the need for high loading, which causes excessive pawl wear. The instantly taught improvement effectively isolates the line pull component by using a hydraulic cylinder in combination with a load sensing device to counterbalance the line pull component, thereby only requiring the levelwind pawl to deal with the friction component of the levelwind.
It is an objective of this invention to provide a cable spooling system having a diamond screw and pawl levelwind in which the pawl is not subjected to the cable load.
Another objective of this invention is to provide a cable winding system with a winding guide in the form of a sheave rotating on an axis oriented at 90 degrees to the spool axis.
It is another objective of this invention to provide a load compensated hydraulic power assisted carriage carrying the sheave and the pawl.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.